Provided is a flush tank device capable of satisfactorily cleaning a toilet bowl. The flush tank device (10) is equipped with a tank body (20) which stores flushing water that cleans a toilet bowl body (1), a water supply device (30) which supplies flushing water to the interior of the tank body (20), and an air suction device (40) which sucks air from the interior of a toilet bowl water drainage duct (3). The air suction device (40) is equipped with an air suction chamber (41) which is formed by partitioning the interior of the tank body (20) and extends in a vertical direction, and the lower end of which opens into the interior of the tank body (20); an air suction opening (47A) which is provided at a location above the water level in the standby state for cleaning the toilet bowl; and an on-off valve (44) which links the air suction chamber (41) to the toilet bowl water drainage duct (3) via this air suction opening (47A), which, if the water surface is at the water level in the standby state for cleaning the toilet bowl, closes the air suction opening (47A), thereby preventing air from flowing into the air suction chamber (41) from the toilet bowl water drainage duct (3) portion, and which, if the water level inside the tank body (20) with the air suction chamber (41) excluded drops below a set water level, opens the air suction opening (47A), thereby permitting air to flow into the air suction chamber (41) from the toilet bowl water drainage duct (3) portion.